The present invention broadly relates to the production of yarn from fibres and, more specifically, pertains to a new and improved method and apparatus for the production of a yarn or the like by means of a friction spinning device.
Generally speaking, the method of the present invention is for spinning a yarn or the like by the open-end friction spinning principle and comprises the steps of: separating fibres from a fibre sliver; transporting the separated fibres in a freely floating condition by means of a pneumatic, fibre-transporting air stream to a moving, perforated surface of a friction spinning means subjected to underpressure; transporting the transferred fibres by means of the moving perforated surface to a yarn formation position in which the transported fibres are formed to a yarn; and withdrawing the formed yarn in a predetermined withdrawal direction.
The apparatus of the present invention is intended for spinning a yarn or the like and comprises: an opening roller of a type employed in open-end rotor spinning; a movable friction spinning means comprising a perforated surface; means for drawing an air stream through the perforated surface of the movable friction spinning means; a fibre feed passage situated between the opening roller and the perforated surface of the friction spinning means for pneumatically transporting fibres from the opening roller to the perforated surface; the fibre feed passage having an exit opening; the exit opening having a longitudinal section; the longitudinal section having longitudinal sides; the longitudinal sides being arranged substantially transverse to a direction of movement of the perforated surface; the fibre feed passage being so inclined in relation to the longitudinal section of the exit opening that the fibres in the pneumatic, fibre-transporting air stream are transported in a direction which is forwardly inclined as viewed in a yarn withdrawal direction; a yarn formation position which is formed on the movable friction spinning means by a lower wall of a suction passage defining a suction zone at a predetermined spacing from the exit opening as viewed in a direction of movement of the movable friction spinning means; and the suction passage being arranged on the perforated surface of the movable friction spinning means opposite to the fibre feed passage and the yarn formation position.
If in friction spinning the fibre sliver is separated into individual fibres by means of an opening or opener roller in a manner similar to that used in rotor spinning, and these fibres are supplied by means of a passage or fibre feed passage towards a friction spinning means, then a disorientation of the fibres can arise in the passage; at least some of the fibres pass towards the exit opening of the passage in a non-straight or bent condition. This disorientation of non-straight or bent fibres is, however, detrimental to an orderly yarn structure, since non-straight or bent fibres, or fibres which may even be kinked or have loops, produce a yarn of relatively low strength and with undesirable irregularity.
A device is known, for example from Swiss Pat. No. 572,108, in which freely moving fibres are fed into converging space between two aspirated rolls rotating in the same sense. The fibres are twisted to a yarn by the rotation of the rolls and are withdrawn by withdrawal rollers provided at the end faces of the rolls.
It is clear that these freely moving fibres must be supplied in a pneumatic feed passage and correspondingly have a final speed which can be about ten times greater than the withdrawal speed of the yarn, so that the fibres arriving in the converging space are braked to a so much lower speed that they assume some kind of loop state or configuration on arrival and these loop states or configurations are substantially retained in the spun yarn.
Loop states or configurations of the fibres in a yarn reduce the strength of the yarn and provide a source of irregularities, since the large number of simultaneously arriving fibres assuming such loop states or configurations produces disorientation or misalignment of the fibres. Furthermore, such a loop state or configuration shortens the useful fibre length. The term "loop state or configuration" of a fibre refers generally to a fibre which is substantially shortened in its above-mentioned useful length through loop formation, bending or kinking.
To a certain degree, stretching of the yarn, and thus also stretching of the individual fibres, is produced by the withdrawal of the yarn as a result of the retention resistance or force in the convergent space or throat of the two drums; this however is insufficient to enable the properties of such a yarn to compare, for example, with those of a ring-spun yarn, so that this type of spinning is suitable substantially only for production of coarser yarns with a statistically better distribution of the individual weak points. The term "coarser yarns" refers generally to yarns used primarily for the production of decorative materials.
In relation to new spinning methods, for example friction spinning, efforts are directed to production of yarns which can be used for the clothing industry, since these yarns represent the greatest proportion, that is up to 60%, of all produced yarns.
In order to substantially avoid the previously mentioned loop states or configurations of the fibres, that is, in order to feed the fibres to the yarn end in a substantially stretched-out or straight state or configuration, the German published Pat. No. 3,300,636, published July 12, 1985, proposes an open-end friction spinning device with two rolls driven in the same sense and arranged closely mutually adjacent to form a wedge-shaped gap or throat, at least one of which rolls is constructed as a suction roll. A feed passage opens onto this suction roll and is arranged in the peripheral direction of the suction roll, in a predetermined spaced relationship, to the wedge-shaped gap. Furthermore, the edge of the feed passage opening directed towards the wedge-shaped gap is formed as a diverting guide for the delivered fibres. This formation is intended to ensure that the fibres are braked at the diverting guide while they are drawn out of the feed passage by means of the suction roll, and thus are subjected to a mechanical stretching. This mechanical stretching effect is intended to lead to an improvement in the laying down of the fibres.
However, the disadvantage of such a device is that, on the one hand, the fibres are subjected to friction, without which this stretching can not be achieved, and that, on the other hand, edges of the device generating such friction are subjected to the danger of contamination, so that occasionally an accumulated clump of dirt may be carried along by the passing fibres and can produce irregularities in the yarn.